I noticed my coolant was low at last oil change so I refilled it. I drove the car (1982 300TD) for 1500 miles and noticed it was about a quart low. I just figured I overfilled or something. I drove it for about 200 miles noticed it was low again. When I checked it yesterday it was right at the line but had bubbles in it, I just got home after a 45 mile drive. Normal pressure when I take the radiator cap off also. I let the car sit for 30 minutes and started it up again and no bubbles. I just wondered if it could be a head gasket or something. Car has 217,000 miles. Starts up and just a little black smoke. Thank you